Fast pulse thermal cautery probe

ABSTRACT

A miniaturized, endoscopically deliverable thermal cautery probe for cauterizing internal vessels. The probe is applied to tissues cold, and a large number of electric heating pulses of equal energy are then applied to an internal heating element in the probe. The probe has an internal heating element in direct thermal contact with an active heat-transfer portion that has a low heat capacity to insure quick heating and subsequent cooling, thereby adequately coagulating tissue while minimizing heat penetration and resulting tissue damage. The electrical power applied to the probe is continuously measured and is terminated when the energy delivered reaches a preset value. The number of such pulses applied to the probe (and hence the total energy delivered) may be preset while the duration of the period during which the pulses were applied is displayed. Alternatively, the duration of the period during which such pulses are applied to the probe may be preset while the number of pulses applied (and hence the total energy delivered) is displayed. The heating element for the probe is a controlled breakdown diode which has a breakdown voltage that is a function of its temperature so that the temperature can be controlled. The heating element has a resistance of greater than 0.5 ohm to provide adequate power dissipation with relatively low currents. A washing fluid, preferably flowing along the outside of the probe toward its tip, cleans blood from the tissue to be coagulated to make the source of blood more readily visible.

The invention described herein was made in the course of work under agrant or award from the U.S. Department of Health, Education andWelfare. The U.S. Government has rights in the invention pursuant toContract No. NO1 AM-5-211 and Research Project Grant RO1 GM-2526.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.285,366, filed July 20, 1981, now U.S. Pat. No. 4,449,528, which is acontinuation-in-part of U.S. patent application Ser. No. 131,897 filedMarch 20, 1980 and now abandoned.

TECHNICAL FIELD

This invention relates to the coagulation of vascularized tissues, andmore particularly to a miniaturized thermal cautery probe which isendoscopically deliverable and which applies precisely controlled heatto such tissues during a relatively short period.

BACKGROUND PRIOR ART

The use of heat for the cauterization of bleeding wounds dates back toancient times. Perhaps the simplest and most basic thermal cauterizationtechnique involves the application of a hot iron to a bleeding wound.While this technique is somewhat effective in cauterizing large,external wounds, the technique is not applicable to internal wounds. Noris the technique sufficiently precise or delimited to provide adequatecauterization without excessive tissue damage.

In the present century, the use of radio frequency electric currenttraveling through a portion of the body has been widely used to stopbleeding. The essential ingredient in radio frequency cauterization isthe dissipation of electrical energy in resistive tissue. Thisdissipated electrical energy is converted into heat, which produces arise in temperature of the tissue and blood. The plasma proteins inblood are denatured in a temperature range of from 50° to 100° C.,producing a sticky or congealed mass of protein. This process isfamiliar in the cooking of egg white. Other processes may take placewhen tissue is heated. For example, vessels may contract or shrink,thereby further reducing the flow of blood.

Several radio frequency current generators are now commerciallyavailable and are widely used by surgeons for both cutting andcoagulating tissue. Since the electrical current flow follows the pathof least resistance, the resulting thermal damage, or necrosis, may attimes be unpredictable, too deep and uncontrolled. The rationale forusing radio frequency current for bleeding control is that the frequencyis above that which would cause neuromuscular stimulation and yet permitsufficient power dissipation to produce a rapid rise in temperature.Thus, used properly, electrical shock does not occur and coagulation isaccomplished.

There is currently much interest in the control of bleeding using themodern fiberoptic endoscope, which permits visualization and therapy inhollow organs of the body through a slender tube. Hollow channels with afew millimeters of inside diameter permit the insertion of instrumentsfor the administration of therapy such as the coagulation of bleeding.Some investigators have reported good success using radio frequencycoagulation through the endoscope in a clinical setting. But thistechnique has not been widely used in practice because of its inherentrisks. Several groups have directed a laser beam through an endoscopeusing a special optical wave-guide with good success in both animals andhumans. However, the high cost of laser coagulators and the as-yetunproven benefit in a controlled clinical trial are slowing thewidespread adoption of this technique. Other problems associated withlaser coagulators arise from the difficulty in precisely directing thelaser beam to a moving target, the existence of optical hazards and theneed for a gas injection system to wash away overlying blood.Furthermore, simple laser coagulators do not simultaneously apply heatand pressure to the wound; and the combination of heat and pressure isconsidered to be more effective than heat alone.

More recently, a miniaturized thermal probe has been developed which isendoscopically deliverable. This probe, which is described in an articleby Protell, et al., "The Heater Probe: A New Endoscopic Method forStopping Massive Gastro-Intestinal Bleeding" Gastroenterology, 74:257-62 (1978), includes a heating coil mounted in a small cylindricalbody with a thermocouple. The output of the thermocouple is compared toa temperature reference level, and the difference is used to control thepower to the probe to achieve a preset probe temperature. In use, theprobe is heated to the preset value and applied to the wound for anumber of periods, each of approximately one second in duration.Alternatively, the cold probe is applied directly to the bleeding site,turned on and held there for a predetermined period after reaching atarget temperature. The principal problem associated with the lattertechnique is the inability of the probe to reach coagulating temperaturewith sufficient speed and to then cool itself with sufficient speed toprevent excessive penetration of the heat by diffusion. Effectivecoagulation requires that the bleeding site be adequately heated.However, avoidance of thermal necrosis requires that the heat notpenetrate too deeply. The only technique providing adequate heating ofthe bleeding site without producing excessive heat penetration isheating the bleeding site at a high temperature for an extremely shortperiod of time. Presently existing thermal probes are not able to meetthese requirements. The problem does not stem from an inability to heatthe probe with sufficient speed as much as it does from an inability tocool the probe with sufficient speed. Any probe can be heated rapidly bymerely utilizing a sufficiently larger heater. However, the probe can becooled only by the tissue with which it is in contact. Conventionalprobes have been incapable of being cooled by the surrounding tissuewith sufficient speed due to their relatively high thermal mass.

Attempts have been made to design thermal cautery probes which areheated by passing a current through the body of the probe itself insteadof through a separate heating element. An example of such probes isdisclosed in U.S. Pat. No. 3,886,944, issued to Jamshidi. Thedisadvantages of such probes are twofold: first, the unavailability of asatisfactory probe material and, second, the nonuniformity of the probetemperature.

The choice of a probe material presents a problem because the resistanceof the material must be high enough to dissipate sufficient power andthe strength of the material must be high enough to withstand forcesapplied to the probe by the tissue and other objects. The Jamshidi probeutilizes a Nichrome alloy or stainless steel as the probe material.Either material has a relatively low resistivity, thereby making itdifficult for the probe to dissipate sufficient power without applying agreat deal of current to the probe. While probes requiring high currentare acceptable under some circumstances, they are uncceptable where theprobe is to be endoscopically deliverable since the high currentsrequire wires which are larger than the endoscope channels. In fact, aprobe having a resistance less than about 0.5 ohm will generally requiremore current than endoscopically deliverable power leads are capable ofcarrying.

A probe fabricated of a low-resistivity material can dissipate adequatepower from relatively low current only by making the material extremelythin so that the resistance of the probe is high. Yet a probe having anextremely thin shell does not have sufficient strength to withstandclinical use.

A probe having a relatively thick shell of a higher resistivity orsemiconductive material would be capable of dissipating adequate powerat acceptably low currents. However, a material having these propertiesand which is inexpensive, easily worked, and sufficiently sturdy doesnot appear to be available.

The second disadvantage mentioned above--the nonuniformity of probetemperature--is illustrated in the Jamshidi patent. In the Jamshidiprobe, current flows outwardly from the center of the probe tip and thenalong the sides of the probe. The current density--and hence the powerdissipation--varies from a maximum at the center of the probe to aminimum at the sides of the probe. As a result, the temperature of theprobe decreases from a maximum at the center of the probe.

DISCLOSURE OF THE INVENTION

The primary object of the invention is to provide a thermal cauteryprobe having a heat capacity which is sufficiently low to allow rapidheating and cooling, thereby effectively coagulating vascularized tissuewithout undue thermal necrosis.

It is another object of the invention to provide a thermal probe whichis powered for a predetermined period while measuring and displaying thetotal energy delivered to the probe during that period.

It is another object of the invention to provide a thermal cautery probewhich is powered by a relatively low current.

It is another object of the invention to provide a low thermal masscautery probe which has a uniform temperature distribution.

It is still another object of the invention to provide a thermal probewhich receives a predetermined value of energy while measuring anddisplaying the duration of the period during which the energy isdelivered.

It is yet another object of the invention to provide a low heat capacitycautery probe which receives energy over a relatively short period inthe form of a large number of relatively short, equal energy pulses.

It is another object of the invention to provide a heating element for athermal cautery probe which inherently provides an indication of thetemperature of the probe's active heat transfer portion.

It is a further object of the invention to provide a washing system fora thermal cautery probe which effectively washes blood from the woundwithout interfering with cauterization, thereby facilitatingidentification of the bleeding site.

It is a still further object of the invention to provide a thermalcautery probe which does not have a tendency to adhere to coagulatedtissue.

These and other objects of the invention are provided by an electricallypowered thermal probe including an active heat-transfer portion having alow heat capacity which is in direct thermal contact with a heatingelement so that heat is transferred principally by conduction. The probeis heater active during a heating period having a duration of less thanfive seconds. Yet sufficient power is applied to the heat-transferportion during the heating period to coagulate tissue, and the low heatcapacity of the heat-transfer portion allows rapid cooling after theheating period. The effective impedance of the heater is greater than0.5 ohm so that the heater can be powered through power lines that arecapable of extending through the channels of an endoscope. The energy isdelivered in the form of a large number of relatively short pulses, eachdelivering the same quantity of energy to the probe. The probe may beused in either of two modes. In a first mode the energy to be deliveredto the probe is preset and the duration of the period during which thepulses are delivered is displayed. Accordingly, a down-counter is presetto a number indicative of the energy to be delivered, and each heatingpulse decrements the down-counter until a zero count is reached. Duringthis period, an oscillator is gated to an up-counter and the contents ofthe counter is displayed to indicate the duration of the period duringwhich the heating pulses were delivered. In a second mode, the durationof the period that the heating pulses are applied to the probe ispreset, and the energy delivered to the probe is displayed. Accordingly,the down-counter is preset to a number indicative of the period duringwhich the pulses are to be delivered, and an oscillator is gated to thedown-counter when the pulses are being delivered until a zero count isreached. Meanwhile, the heating pulses are applied to the up-counter,and the contents of the counter is displayed to indicate the energydelivered to the probe during the heating period. The heating elementfor the probe is preferably a controlled breakdown diode, such as azener or avalanche diode, which provides good heat dissipation at lowcurrents and has a breakdown voltage which is temperature dependent sothat it provides an electrical indication of probe temperature. Theprobe temperature indication is used to inhibit the delivery of heatingpulses to the probe where the temperature of the probe exceeds a targetvalue. A plurality of water jets, which are circumferentially spacedabout the body of the probe, direct water along the probe sidewalls inan axial direction, thereby clearing blood from the bleeding site.Finally, the end of the probe is coated with a special compound toprevent the probe from adhering to coagulated tissues.

In operation, one of the two operating modes is selected and thecauterization time or cauterization energy is preset, depending uponwhich mode is selected. The probe is then applied to the wound whilecold, and a switch is activated to apply power to the probe. The lowheat capacity of the probe's active heat-transfer portion allows it toquickly reach a sufficient temperature to effectively cauterize thewound and to rapidly cool after power is removed to prevent excessivethermal penetration, thereby minimizing necrosis.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of the fast pulse thermal cautery probe inoperation;

FIG. 2 is an exploded isometric view of the thermal cautery probe;

FIG. 3 is an isometric view of the assembled thermal cautery probe;

FIG. 4 A and B is a schematic of the circuitry for supplying power tothe thermal cautery probe;

FIG. 5 is a cross-sectional view taken along the line 5--5 of FIG. 3.;and

FIG. 6 is a graph showing the temperature at the heat transfer surfaceof the probe.

BEST MODE FOR CARRYING OUT THE INVENTION

The fast pulse thermal cautery probe is illustrated in use in FIG. 1.The probe includes a power supply and display unit 10 having a frontpanel 12 containing switches and indicators illustrated in greaterdetail in the enlarged view. A specially constructed catheter 14 extendsfrom the power supply and display unit 10 to a headpiece 16 of aconventional fiberoptic endoscope 18 extending into the mouth of apatient P to, for example, the patient's stomach. The headpiece 16typically includes an eyepiece through which a surgeon S views internalcavities. However, the headpiece 16 may alternatively interface withvarious optical devices of conventional design. These devices mayproduce an image on a screen 20 of the position of the probe 22 withinthe stomach of the patient P. The endoscope 18 typically includes one ormore passages or channels extending in parallel with the fiberoptic waveguide to allow various devices to be inserted into internal organs of apatient. The catheter 14 extends through one of these channels to theend of the endoscope 18 within an internal organ. A surgeon S may thenposition the probe 22 against a lesion such as an ulcer by manipulatingactuator knobs generally positioned on the headpiece 16 of conventionalendoscopes 18. The endoscope channels are necessarily limited indiameter so that the diameter of the power leads for applying power tothe probe are also limited. In practice, the diameter of the power leadsis limited to a size which is capable of delivering sufficient currentfor cauterization to a probe having a resistance of at least about 0.5ohm. A probe having a lower resistance must receive a current which isin excess of that which endoscopically deliverable power leads arecapable of efficiently carrying without producing excessive heating ofthe endoscope.

A foot switch 28 is also connected to the power supply and display unit10 through a lead 29. As explained in greater detail hereinafter, thesurgeon S actuates the foot switch 28 to apply power to the probe 22after the probe has been applied to the lesion. A second switch,operating in conjunction with the switch 28, may be actuated to supply awashing fluid to the probe.

As best illustrated in the enlarged view of FIG. 1, the panel 12includes an on-off switch 30 for applying power to the unit 10 and amode switch 32 for selecting either a "time" mode or an "energy" mode.In the time mode, heating pulses are applied to the probe 22 for aperiod having a duration determined by the number preset withconventional thumb wheel switches 34. At the end of the period, thetotal energy delivered to the probe 22 during that period is shown on aconventional digital indicator 36. In the energy mode, the energy to bedelivered to the probe each time the switch 28 is activated is seletedby the thumb wheel switches 34, and the duration of the period duringwhich the pulses are delivered is shown on the indicator 36. Thetemperature of the probe during the heating period in either mode isselected by a temperature control knob 33.

The probe 22 is illustrated in assembled condition in FIG. 3. It iscomposed of an elongated cylindrical shell 40 having a smooth,round-ended forward portion and a cylindrical body 42 containing anumber of circumferentially spaced-apart cleaning fluid nozzles 44. Thecatheter 14 abuts the body 42 of the probe 22 and supplies cleaningfluid to the nozzles 44 and heating pulses to an internal heatingelement in the shell 40, as explained in greater detail hereinafter.

The internal structure of the probe 22 is illustrated in greater detailin FIGS. 2 and 5. This structure is best explained in the context of themanufacturing procedure for the probe. Initially, a coaxial cable 50 isprepared by trimming a portion of an insulating sheath 52 back from anunderlying coaxial metal braid 54, a coaxial dielectric insulator 56 anda center conductor 58. In a similar manner, the braid 54 is trimmed backfrom the underlying insulator 56 and conductor 58, and the insulator 56is trimmed back from the underlying conductor 58. As a result, eachcomponent of the cable 50 is accessible.

After the cable 50 has been prepared as explained above, the body 42 ofthe probe 22 is loosely slipped over the cable 50, and the insulator 56and center conductor 58 are inserted through a bore 60 of a coaxialbraid anchor 62 with the braid 54 loosely fitting inside a cylindricalportion at the rear of the braid anchor 62. The braid 54 is thensoldered to the walls of the bore 60 by conventional means toelectrically and mechanically connect the braid anchor 62 to the braid54 of cable 50.

A spring mount 102 is then soldered to the coax center conductor 58 anda spring 100 is soldered onto the spring mount 102. Next, the braidanchor 62 is slipped into the body 42 with resilient fingers 109 of thebraid anchor 62 frictionally engaging the inside surface of the body 42.Next the assembly is placed in a vertical position and a small amount ofepoxy is applied between spring mount 102 and braid anchor 62 to form aseal 70 having a shoulder 72. The seal 70 provides electrical insulationand a seal to prevent fluids from entering the internal cavity of theprobe. A teflon seal 108 is then pressed into body 42 with the shoulderon seal 108 resting against the fingers 110 of body 42. The spring 100now lies inside of the cylindrical bore 106 of seal 108 with the axialtip 105 of spring 100 protruding from the bore 106 a small amount.

After the rearward components of the probe 22 are prepared and assembledas explained above, the internal components of the shell 40 areassembled. As best illustrated in FIG. 5, the shell 40 is generallyhollow to form a cylindrical cavity 80 surrounded by thin, cylindricalside walls 82. The front end of the shell 40 is a solid hemisphericalheat transfer portion 84 having a planar, circular rear face 86. Acontrolled breakdown diode, such as a zener or avalanche diode 90, isthen bonded within the cavity 80 against the rear face 86. The diode 90includes a diode chip 92, a pair of cylindrical conductors 94, 96connected to opposite faces of the diode chip 92, and an insulativecoating 98 surrounding the diode chip 92 and conductors 94, 96. Althougha diode 90 having the structure shown could be specially fabricated, thediode 90 is preferably formed by severing the ends of commerciallyavailable diodes having a cylndrical shape. A simpler and easiertechnique would be to solder a commercially available diode chipdirectly to cavity 80 against the rear face 86, although other heatingdevices such as a thin film resistor or conventional diode, may also beused. However, such alternative heating devices generally requiresubstantially more current to dissipate the same amount of power. Forexample, a 14-volt zener diode dissipates about twenty times more powerfor a given current than a diode having 0.7-volt forward breakdownvoltage.

The diode 90 is mounted in the shell 40 by first tinning the rear face86 of the heat transfer portion 84 with solder. The exposed surface ofone diode conductor 94 is then also tinned and placed in the shell 40,preferably using an alignment jig to position the diode 90 at the centerof the shell 40. The shell 40 is then heated to fuse the solder on therear face 86 and the solder on the diode conductor 94. The diode 90 isthus in direct thermal contact with the heat-transfer portion 84 so thatheat is transferred from the diode 90 to the heat-transfer portion 84principally by conduction rather than by radiation.

After the diode 90 is soldered within the shell 40, the outer surfacesof the shell 40 are polished and then plated with copper and gold.Finally, a conformal coating is applied to the outer surface of theshell 82 to prevent it from sticking to tissues after coagulation. Thecoating is preferably Type R-4-3117 sold by Dow-Corning which isnormally used to seal printed circuit boards from moisture and abrasion.The coating should be applied over an undercoat of Dow Corning 1204Primer for best adhesion of the conformal coating to the probe.Alternatively, the primer may be used without the conformal coating,providing the probe with better heat transfer characteristics to tissuebut having a greater tendency to adhere to coagulated tissues.

In a final assembly stage, the shell 40 is moved rearwardly untilresilient fingers 110 of the body 42 frictionally engage the inner walls82 of the shell 40. Finally, as illustrated in FIGS. 3 and 5, a catheter112, loosely surrounding the cable 50, is slipped onto a shoulder 114(FIG. 5) formed along the rear edge of the body 42, thereby completingthe assembly of the probe.

A washing fluid is pumped through the catheter 112 around the cable 50and enters rear openings of the nozzles 44. The washing fluid then flowsalong the side of the shell 40 in an axial direction to wash blood fromthe lesion, thereby facilitating the identification of bleeding sites inneed of coagulation. A variety of commercially available pumps may beused to deliver washing fluid to the probe. However, the fluid ispreferably delivered in a pulsating fashion to allow sufficient bleedingbetween washing pulses to make the site of bleeding readily visible.

It is highly advantageous to run the washing fluid along the outside ofthe shell for a number of reasons. First, the washing fluid does notpass between the heat transfer portion 84 of the probe and the tissue tobe coagulated. Consequently, it does not interfere with the transfer ofheat from the probe to the tissue. Second, the washing fluid flows alongsurfaces which do not contact tissue and are thus not susceptible totissue clogging which would interfere with fluid flow. Finally, thefluid stream is spread out over a sufficiently large area to preventtissue damage which might otherwise occur with a more concentrated fluidstream.

In the probe's assembled condition, the conductor spring 100 is somewhatcompressed so that the point 105 forcibly contacts the conductor 96. Thediode conductor 94 is connected to the shell 40 and, in turn, to thebraid 54 through the body 42 and braid anchor 62. Thus, as currentpulses are applied between the center conductor 58 and the braid 54 ofcable 50, current flows through the semi-conductor junction 92, whichquickly heats the heat transfer portion 84. Because of the low heatcapacity of the heat transfer portion 84, the portion 84 not onlyquickly rises to a target temperature, but it also quickly cools afterheating pulses are no longer applied to the probe 22.

The circuitry for generating the heating pulses is illustrated in FIGS.4A and 4B. With reference first to FIG. 4B, the foot switch 28, in its"off" position, places a logic low at one input to a set-reset flip-flopformed by NAND gates 200, 202. Consequently, the output of NAND gate 200is high, while the output of NAND gate 202 is low since its other inputis biased high through resistor 204. When the switch 28 is moved fromthe "off" position, the output of NAND gate 200 is held high by the lowat the output of NAND gate 202 since its other input is biased highthrough resistor 206. When the switch 28 is actuated to the "on"position, the output of NAND gate 202 goes high, thereby causing theoutput of NAND gate 200 to go low. The negative-going transition at theoutput of NAND gate 200 is differentiated by capacitor 208 and appliedto the preset (ps) terminal of flip-flop 210, which is normally heldhigh through resistor 212. The Q output of flip-flop 210 then goes highto produce an ENABLE signal. It will be noted that a negative-goingtransition will not be generated at the output of NAND gate 200 untilthe switch 28 is returned to its "off" position and once again cycled toits "on" position. Consequently, any contact bounce present in switch 28as the switch reaches its "on" position, has no effect on the operationof the circuit.

The ENABLE signal generated by flip-flop 210 has a number of functions.First, it presets cascaded counters 220a,b,c with numbers selected bythe thumbwheel switches 34a, b,c, respectively. The data inputs to thesecounters 220 are normally held low through resistors 222, but theselines are driven high by the switches 34 so that the BCD numbers appliedto each of the counters 220a,b,c correspond to the decimal numbersappearing on the panel 12 of the power supply and display unit 10.

The enable input also enables a synchronous oscillator 226 formed by aone-shot, which generates a pulse train having a frequency determined bythe time constant of resistor 227 and capacitor 229 and the timeconstant of resistor 231 and capacitor 233. The ENABLE signal is alsoinverted by enabled NAND gate 228 to produce a negative-going transitionwhich is differentiated by capacitor 230 and resistor 232 to generate anegative-going reset pulse which resets counters 234a,b,c. Thus,actuation of the foot switch 28 resets up-counters 234a,b,c, presetsdown-counters 220a,b,c with a number selected by thumb wheel switches34a,b,c and allows oscillator 226 to begin decrementing thedown-counters 220a,b,c.

With reference now to FIG. 4A, the ENABLE signal is also applied to NANDgate 240 to initiate the delivery of heating pulses to the probe 22.Assuming that the other input to NAND gate 240 is high, the low to hightransition of the ENABLE signal sets flip-flop 242 so that its Q outputgoes low. Current then flows through resistor 244 and light-emittingdiode 246. The light-emitting diode 246 is optically coupled to aphototransistor 248 which saturates to drive transistor 250 tosaturation so that a negative power supply voltage is applied directlyto the diode 90 through a fairly low impedence resistor 252. The voltagesupplied to the diode 90 is applied to a conventional integrated circuitmultiplier 254 after being attenuated by resistors 256, 258 arranged ina voltage divider configuration. The voltage on the opposite terminal ofthe resistor 252 (which exceeds the voltage on diode 90 by a function ofthe current-through diode 90) is similarly applied to the multiplier 254after being attenuated by resistors 260, 262 arranged as a voltagedivider. The multiplier 254 generates a voltage which is proportional tothe product of the voltage applied to the diode 90 and the voltageacross the resistor 252. Since the voltage across resistor 252 isproportional to the current-through diode 90, the voltage at the outputof the multiplier 254 is proportional to the power being applied to thediode 90. This power signal is applied to an operational amplifier 264through resistor 266. The operational amplifier has a capacitor 268connected in its feedback path so that it operates as an integrator. Theintegrated power signal at the output of the amplifier 264 is thus avoltage proportional to the energy which has been delivered to the diode90 from the end of the last COUNT pulse. The energy signal at the outputof amplifier 264 is compared by a comparator 280 to an energy referencesignal generated by potentiometer 282. When the energy delivered to thediode 90 exceeds a value determined by the potentiometer 282, the outputof the comparator 280 goes low, thereby actuating a one-shot 284 throughresistor 286. The trigger input to the one-shot 284 is normally heldhigh through resistor 288 and the resistor 286. The one-shot 284 clearsor disables the flip-flip 242 for a predetermined period determined bythe time constant or resistor 290 and capacitor 292.

During this disabling period, the Q output of flip-flop 242 is high,thereby causing amplifier 294 to clip at its negative supply level. Thisnegative voltage back-biases diode 298, thereby floating the gate of FETtransistor 296. The source to drain impedance of the FET 296 is thengreatly reduced, thereby discharging capacitor 268 and reducing theoutput of the power signal integrator 264 to zero volts. At the end ofthis COUNT pulse (after the disable period as determined by one-shot284), the Q output of flip-flop 242 once again goes low, causing theoutput of amplifier 294 to float so that the gate of FET 296 is heldhigh through resistor 300. The source to drain impedance of the FET 296then increases sufficiently to allow the amplifier 264 to once againintegrate the incoming power signal. The amplifier 294 thus functions asa level converter to interface the logic circuitry of the flip-flop 242to the voltage levels required by the FET 296. It switches between thesetwo voltage levels at a voltage determined by resistors 302, 304, whichare arranged in a voltage divider configuration.

At the end of the fifty microsecond disable period, flip-flop 242 isonce again set, thereby once again saturating transistors 248, 250 andapplying power to the diode 90. It is thus seen that as long as a logic"0" is applied to the set terminal of flip-flop 242, measured quantitiesof energy are sequentially applied to the diode 90 in a pulse train.

The foregoing explanation of the circuit operation presupposes that bothinputs to NAND gate 240 are logic "1" during the operating cycle. Thiswill always be the case as long as the temperature of the diode 90 isbelow a preset value. However, NAND gate 240 is disabled as long as thetemperature of the diode 90 exceeds the predetermined value.Consequently, the temperature of the probe 22 quickly rises to thepredetermined value as current pulses are repetitively applied to thediode 90; and when the predetermined level is reached, the pulses areapplied to the diode 90 at a lower frequency to maintain the temperatureconstant.

In accordance with this feature, a by-pass resistor 301 is positionedbetween the base and emitter of transistor 250 so that a slight amountof current flows through diode 90 when transistors 248 and 250 are cutoff. Diode 90 is preferably an avalanche diode, and its reversebreakdown voltage is proportional to its temperature. Consequently, thevoltage between resistors 256 and 258, which is applied to a temperaturecomparator 302 is a measure of the temperature of the diode 90. Thistemperature feedback voltage is compared to a reference voltagedetermined by resistors 303, 306 and potentiometers 308, 310 and thetemperature controller potentiometer 33. Potentiometer 308 is varied toadjust the bias on field effect transistor 312, thus adjusting the slopeof the temperature-to-voltage transfer curve. The potentiometer 310 isadjusted to set the 0° C. Intercept on the curve, thereby calibratingthe temperature selector 33. When the temperature, as indicated by thevoltage on the positive input to the comparator 302, exceeds the levelset by potentiometer 33, its output goes low so that a low is placed onthe input to NAND gate 240 through resistor 316. Thereafter, noadditional current pulses can be applied to the diode 90 until thetemperature falls below the preset value. The temperature comparator 302then generates a logic "1" to enable the NAND gate 240.

Returning now to FIG. 4B, when the switch 32a is in the "energy"position as illustrated, the COUNT pulses produced each time a currentpulse is applied to the probe 90 are inverted by enabled NAND-gate 330and applied to the first counter 234a of a series of cascaded counters234a,b,c. It will be remembered that these counters 234 had been resetto zero by the leading edge of the ENABLE signal when the switch 28 wasinitially actuated. At the termination of each current pulse to thediode 90, the counters 234 are incremented by a COUNT pulse. Thus, thecontent of the counters 234 is an indication of the total energy whichhas been applied to the probe 90 during the ENABLE pulse. The counters234 drive the front panel three-digit readout 36 which then continuouslyindicates the energy which has been applied to the probe 90.

As long as the ENABLE signal is present, the oscillator 226 continuouslygenerates timing pulses regardless of the frequency at which currentpulses are applied to the diode 90. When the switch 32b is in the timeposition indicated, these pulses are applied to the first counter 220aof a series of down-counters 220a,b,c. As mentioned above, the leadingedge of the ENABLE pulse presets the counters 220 with a numbercorresponding to the number selected by the thumb wheel switches 34 ofthe front panel 12. The counters 220 thus begin counting down from thisnumber until a zero count is reached. Upon the zero count from counter220c, a high is produced at the output of enabled NAND-gate 332 whichclocks a logic "0" on the data input (D) of flip-flop 210 to its Qoutput, thereby terminating the ENABLE pulse. The ENABLE line is nowlogic "0", thereby disabling the oscillator 226 so that counters220a,b,c are no longer decrementing. The ENABLE low also removes the lowfrom the set input to flip-flop 242 (FIG. 4A), thereby allowing its Qoutput to remain high in order to prevent COUNT pulses from beinggenerated which would otherwise cause additional current pulses to beapplied to the diode 90 and increment the counters 234a,b,c. It is thusseen that when switch 32 is in the "time" position illustrated, theswitches 34 select the duration of the period during which currentpulses are applied to the probe 90, while the front panel three-digitreadout 36 indicates the total quantity of energy delivered to the diode90 during that period.

Repositioning the switch 32 to the "energy" mode causes the timingpulses from oscillator 226 to be applied to the up-counters 234 whilethe COUNT pulses generated for each heating pulse are applied to thedown counters 220. Thus, in this alternate "energy" mode, the switches34 select the total energy to be delivered to the diode 90 while thefront panel three-digit readout 36 indicates the duration of the periodduring which the energy was delivered to the diode 90.

During use of the probe 22, the termination of the heating pulsesapplied to the probe 22 is not visually apparent. Consequently, anaudible alarm may be provided to inform the surgeon when to remove theprobe from the wound area. Accordingly, as illustrated in FIG. 4B, the Qoutput of flip-flop 210 is applied to a one shot 340 and a NAND-gate342. The output of the NAND-gate 342 is applied to a conventional audioalarm 344, commonly known as a "SONALERT".

Prior to initiating an ENABLE pulse, the Q output of flip-flop 210 andthe output of one-shot 340 are both high, keeping the output of NANDgate 342 low so that no current flows through the SONALERT 344. When theENABLE pulse occurs, NAND gate 342 becomes disabled and its output goeshigh, turning on the SONALERT 344. At the termination of the ENABLEpulse, the Q output of flip-flop 210 goes high, thereby triggering theone-shot 340, whose output goes low, keeping NAND gate 342 disableddespite the high input from the Q output of flip-flop 210. When theone-shot 340 output goes high after a period determined by resistor 346and capacitor 348, the NAND gate 342 is again enabled, setting itsoutput low and turning off the SONALERT 344. Thus, the SONALERT 344operates during the ENABLE pulse and for a fixed time longer. This addedtime insures that a complete cycle occurred with the probe in contactwith the lesion, including the time required for the probe-tissueinterface temperature to fall below that for tissue denaturization. Thisis generally on the order of about 0.2 second.

The foot switch 28 may also include a second switch contact 28' which,when closed, applies power to a conventional fluid pump 360 whichdelivers washing fluid to probe. As mentioned above, the pump 360preferably operates in a pulse-like manner to allow a sufficiently longperiod between pulses to identify bleeding sites.

In operation, an endoscopist or surgeon first threads the catheter 14through a channel in an endoscope 18 and manipulates the probe 22 at theend of the catheter 14 until it is in a desired position against thewound. Either thereafter or before, the surgeon S has selected either atime or an energy mode, and he has selected either a predeterminedduration of cauterization or cauterization energy, respectively, onthumb wheel switches 34. Finally, the surgeon S rotates temperaturepotentiometer 33 to select a predetermined temperature. The surgeon thenactuates the foot switch 28 to cauterize the wound or deliver washingfluid to the wound. In the time mode, the energy applied to the probe 22during the heating period is displayed on the readout 36. In the energymode, the duration of the cauterization period is displayed on thereadout 36. The probe 22 is then repositioned a number of times, afterwhich the switch 28 is actuated to cauterize various portions of thewound.

The temperature characteristics of the probe may be examined withreference to FIG. 6. As clearly illustrated therein, the probe reaches atarget temperature in less than one-fourth of a second, remains fairlyconstant thereafter, and drops to less than 50 percent of the targetvalue in less than one second. As a result, it is not necessary to leavethe probe in contact with the wound for a long period in order toeffectively cauterize the wound, so deep thermal penetration, and hence,thermal necrosis, do not occur. It has been found that the temperatureof the active heat transfer portion of the probe should be at least 100°C. to provide adequate coagulation in a fairly short time period. It hasalso been determined that deep heat penetration, and hence thermalnecrosis, occurs when a probe having a temperature of at least 40percent of the required temperature contacts tissue for more than 5seconds. Thus the probe must be rapidly heated and rapidly cooled withinthe specified range to adequately coagulate without causing tissuedamage. Rapid heating is not difficult because the power consumption ofthe probe heater can be adjusted as desired. However, probe coolingafter the heating period is provided by heat conduction of the tissuecontacting the probe. Unlike the problem of rapid heating, rapid coolingcan be accomplished only by using a probe having a low heat capacity. Ithas been determined that the probe requirements for sufficiently rapidheating and cooling can be accomplished with a probe having an activeheat transfer portion that has a unit heat capacity of about less than˜1 joule/°C. or, equivalently, a unit heat capacity of less than ˜0.25Cal./°C. Probes having a larger heat capacity run the risk of causingdeeper damage if effective coagulation is achieved.

Although the device described herein is principally designed forcauterization, it will be understood that it may also be used for othertypes of treatment. For example, it may be used to destroy superficialskin cancers without causing deep tissue damage. Consequently, the scopeof the invention is not to be limited by the field to which theinvention is applied.

We claim:
 1. A probe for heating tissue, comprising a probe body havinga heat conductive portion forming an external heat-transfer surfaceadapted to be placed in contact with said tissue, a diode mounted insaid probe body in thermal contact with said heat conductive portion sothat electricity flowing through said diode generates heat that isconducted through said heat-conductive portion to said heat-transfersurface, said diode having a reverse breakdown voltage that isproportional to its temperature, and a power supply connected to saiddiode through a conductor, said power supply having a polarity thatcauses reverse current to flow through said diode, said power supplyincluding means for adjusting the power that said power supply deliversto said diode responsive to variations in the magnitude of said reversebreakdown voltage in order to control the temperature of said probe. 2.The probe of claim 1 wherein said probe body comprises a generallycylindrical, electrically conductive shell having said heat-conductiveportion formed at one end and a cylindrical cavity having an opening atthe opposite end, and wherein said diode is mounted in said cavity indirect thermal contact with said heat-conductive portion.
 3. The probeof claim 2 wherein the diode mounted in said cavity has a pair ofopposed planar conductive faces, one of which is soldered to theheat-conductive portion of said shell, said probe further including anelectrically conductive spring in electrical contact with the conductorthat is connected to said power supply, said spring bearing against theother face of said diode, thereby supplying electrical power to saiddiode.
 4. The probe of claim 1 wherein said heat-transfer surface iscoated with a low-adhesion material to prevent said heat-transfersurface from sticking to tissue.
 5. The probe of claim 1 wherein saiddiode is a zener diode so that the power generated by said diode inoperation is proportional to the product of the zener voltage of saiddiode and the current through said diode.